In the first half of the 20th century, ribbon microphones once dominated commercial broadcasting and recording industries as a preferred high-end microphone technology. First developed by Dr. Harry F. Olson of RCA corporation in the late 1920's, Ribbon microphones widely commercialized in the 1930's exhibited superior frequency responses and higher-fidelity output signals compared to many condenser microphones of the time.
A ribbon microphone typically uses a thin piece of metal immersed in magnetic field generated by surrounding magnets. The thin piece of metal is generally called a “ribbon” and is often corrugated to achieve wider frequency response and fidelity. Ribbon microphones became vastly popular and became a primary broadcasting and recording microphone until mid-1960's.
However, the classic ribbon microphone architecture was susceptible to significant disadvantages. First, a typical ribbon microphone contained a fragile ultra-thin ribbon, typically made of corrugated aluminum, which could break easily if the ribbon microphone casing was subject to a gust of air through its microphone windscreen. Second, most ribbon microphones could not produce as high output signal level as condenser or dynamic microphones. The lack of high output signal level for ribbon microphones usually required careful pre-amplification matching and tuning, which was cumbersome and contributed to reduced ruggedness and reliability compared to condenser and dynamic microphones.
By the mid-1960's, dynamic moving-coil microphones (i.e. coil wire on a diaphragm suspended over a magnetic field) and condenser microphones (i.e. capacitor microphones) evolved technologically for higher sensitivity and signal-to-noise ratio (SNR) to compete effectively against ribbon microphones. For example, improved condenser microphones exhibited substantially higher output signal level than ribbon microphones, thereby simplifying pre-amplification process and improving reliability of recording or broadcasting equipment.
Although a typical condenser microphone had the tendency of exaggerating upper frequency ranges whenever inherent harmonic resonances occurred in a diaphragm of the microphone, the exaggerated upper frequency was actually preferred by some while recording industry continued using analog tape mediums for audio recording. Most analog tapes suffered generational signal losses and could not accurately capture high-frequency ranges, which made the use of condenser microphone-based recording equipment more acceptable. Similarly, although dynamic moving-coil microphones fundamentally possessed higher resistivity to sound waves than ribbon microphones, improved dynamic moving-coil microphones provided ways to compensate for a relatively low high-frequency response. Therefore, by the mid-1960's, most ribbon microphones were rapidly replaced by more portable, rugged, and user-friendly condenser and dynamic moving-coil microphones. By the end of that decade, ribbon microphones were widely considered obsolete.
However, despite several drawbacks as mentioned above, ribbon microphones possess fundamental advantages as recording and broadcasting industry become fully adjusted to the digital era. As Compact Discs and solid-state non-volatile memory (e.g. NAND flash memory) became recording media of choice for highly digitized recording and broadcasting equipment, the high-frequency exaggeration and distortion provided by condenser microphones were no longer desirable. Many audio engineers and music lovers began to favor more natural and linear reproduction of sound, which meant that ribbon microphone's fundamentally higher fidelity in higher frequencies received attention once again. Ribbon microphones also provide a generally richer and fuller sound reproduction compared to condenser and dynamic moving-coil microphones with digital audio recording and broadcasting equipment. In recent years, there has been a resurgence of demand for retrofitted ribbon microphones of yore and a need for newly-designed ribbon microphones, especially in the high-end audio industry.
For a newly-designed microphone, it is desirable to reduce signal distortions, provide a high-fidelity sound-capturing design element for a magnet motor assembly surrounding a ribbon, and simplify circuitry to reduce cost of production. Furthermore, a novel phantom-powered JFET preamplifier gain circuit that can minimize undesirable sound distortions and reduce the cost of producing a conventional preamplifier gain circuit in audio applications is also highly desirable.